In a liquid crystal display device, a thin-film EL (electroluminescence) display device, an organic EL display device or the like, an amorphous silicon (a-Si) film has been conventionally mainly used as a semiconductor film that functions as a channel layer of a TFT (thin-film transistor) which is a semiconductor device.
In recent years, attention has been focused on a composite oxide including indium (In), gallium (Ga) and zinc (Zn), i.e., an In—Ga—Zn-based composite oxide (also referred to as “IGZO”), as an alternative material to a-Si. A higher carrier mobility can be expected in an IGZO-based oxide semiconductor as compared with a-Si.
International Publication No. 2005/088726 (PTD 1) discloses that a field-effect mobility of approximately 0.5 to 10 cm2/Vs is obtained when an amorphous oxide having an electron carrier concentration lower than 1018/cm3 is used in a channel layer of a TFT.
Japanese Patent Laying-Open No. 2008-192721 (PTD 2) discloses an oxide sintered body mainly made of indium and including tungsten, as a material suitably used when forming an oxide semiconductor film by the sputtering method and the like.